Cells coupling together through a nanotube (arrow) (Source: University of Bergen)

Cells use nano-thin membrane tubes and gap junctions to send electrical signals to one another

Researchers
from the University of Bergen's Department of
Biomedicine have discovered new details associated with how cells communicate,
which could eventually contribute to our knowledge of cell activity during
processes like the healing of wounds.

Dr. Xiang
Wang and Professor Hans-Hermann Gerdes, who are researchers from the University
of Bergen's Department of Biomedicine, have studied how electrical signals are
passed from cell to cell, and found that nano-thin membrane tubes and gap
junctions together made it possible for cells to transmit these signals. By
learning how tunneling nanotubes (TNTs) allow cells to couple and communicate,
scientists hope to learn how cells perform certain tasks like developing tissue
in the embryo.

Wang and
Gerdes made the discovery when applying a fluorescent dye to cells that were
connecting through the formation of a nanotube. As the electric potential of
the cell membrane changes, the dye changes in intensity. As two cells formed a
connection through a nanotube, a microinjection needle was used to depolarize
the cell's membrane potential, which made the dye on the cell membrane light
up. On the other end of the nanotube, the fluorescent indicator lit up as well.
Wang noted that this is a characteristic most cells possess, but not all.

The nanotubes only last a
few minutes, which makes it difficult for scientists to figure out when and
where the cells will form the nanotubes. To better track these formations, Wang
and Gerdes created a micro-matrix that consists of "thousands of points
and bridges on a plate surface." Nano-structured material is then placed
on the plate to allow cells to stick. At each point, a cell is placed in hopes
of nanotubes being formed along the bridges, and a camera is used to catch the
creation of nanotubes. The microscope takes 50 preselected pictures every five
minutes.

While it
is important to further understand the formation of the
nanotubes, the nanotubes alone do not allow cells to transmit
electrical signals. According to Wang, gap junctions, which consist of a
ring-shaped proteins, always connect one end of the nanotube to cells before
the cell transmits electrical signals. In some other cases, electrical signals
sent to the membrane of the receiving cell via nanotube enter after the
membrane is depolarized and a calcium channel opens. This helped push the
signals along.

"In
other words, there are two components: a nanotube and a gap junction,"
said Gerdes. "The nanotube grows out from one cell and connects to the
other cell through a gap junction. Only then can the two cells be coupled
electrically."

Wang and
Gerdes hope that this sort of research can lead to the understanding of how
cells group together to heal wounds, and how cells create tissue in the
embryo.

"It's
quite possible that the discovery of nanotubes will give us new insight into
intercellular communication," said Gerdes. "The process could explain
how cells are coordinated during embryo growth. In that phase, cells travel
long distances -- yet they demonstrate a kind of collective behavior, and move
together like a flock of birds can."

The
researchers also hope that to find that this method of electrical impulse
transfer is present in human brain cells. This could lead to a better
understanding of brain function overall.